If your home country is historically heterogeneous and you know it, crack a smile.

People who live in countries built on centuries of migration from a wide range of other countries are more emotionally expressive than people in more insular cultures, according to research led by University of Wisconsin–Madison psychology Professor Paula Niedenthal.

Countries most comfortable with wearing their hearts on their sleeves are likely to also score high in “historical heterogeneity,” a measurement created by a group of Brown University economists to describe the breadth of a country’s migration sources over the last 500 years.

“We think an absence of shared language and shared culture would push people toward greater nonverbal expression of emotion,” Niedenthal says. “Because otherwise you wouldn’t know what the other person was feeling or thinking or liking or disliking. And you need to be able to communicate those things to facilitate commerce and government, to survive and prosper together.”

The United States sits high up on the measure of historical heterogeneity, with Canada, Australia, Brazil and Uruguay. The homogenous end of the spectrum includes Greece, Japan, Poland and Nigeria, confounding a geographic interpretation of the cultural differences in emotional displays.

“So many places other than the United States have a long history of migration — many in South America, places like Israel — and that creates an idea about who should be similar or dissimilar that isn’t one we currently look at,” Niedenthal says. “The dominant way to think about culture right now in industry and organizational settings and academia is the notion of collectivism versus individualism, and that’s basically West versus East.”

Niedenthal says people who live in countries built on centuries of migration from a wide range of other countries are more emotionally expressive than people in more insular cultures.

Apparently, shaping emotional culture takes time. The researchers compared their emotional expressivity results to another demographic measure of immigration — the sheer number of home countries represented by immigrants living in each of 32 countries in 2013 — and found little correlation.

“In many countries, today’s diversity involves a lot of minority influx,” Niedenthal says. “Those people are often arriving at the bottom of the social ladder, hoping to find work, and people in those positions don’t immediately influence the culture. It takes time and generations and standing for that to happen.”

The economists behind historical heterogeneity were looking for a way to predict income inequality, and Niedenthal believes the influence of long-term migration should turn out to be important in many kinds of social behaviors and even public policy.

“The important issue is imagining all the ways in which cultures created by multiple source countries rather than few source countries differ,” says Niedenthal, whose work is funded by the National Science Foundation. “For example, they may be more or less willing to pay for universal health care, because they empathize differently with in-group and out-group members.”

The researchers also found that despite migratory makeup, relative individualism, residential mobility or ethnic fractionalization, people the world round identify the same three kinds of smiles — reward, affiliation and dominance — and that the frequency with which the three are deployed also vary in neat parallel with a country’s historical heterogeneity.

“Two of the main tasks you could imagine being important to a group of people with mixed cultural backgrounds are affiliation, creating and maintaining social bonds, and reward — telling people what’s good and what’s bad,” Niedenthal says. “In homogenous cultures, they have hierarchies that have been established over the course of many, many generations, and they tend to view dominance smiles as more frequent or important.”